学步园

【I】将给定的字符串转化为相应的整数

/*[1]. atoi 将给定的字符串转换为数字
* int m_atoi(char *strNum)
* @author arhaiyun
**/
bool g_bInvalidInput = false;
int m_atoi(char *strNum)
{
	if(*strNum == '\0')
	{
		g_bInvalidInput = true;
		return 0;
	}
	
	g_bInvalidInput = false;
	
	//确定整数正负
	int flag = 1;
	if(*strNum == '+')
	{
		strNum++;
	}
	else if(*strNum == '-')
	{
		flag = -1;
		strNum++;
	}
	
	int result = atoi_core(strNum, flag)
	
	return result;
}

int atoi_core(char *strNum, int flag)
{
	long long result = 0;
	
	while(*strNum != '\0')
	{
		if(*strNum >= '0' && *strNum <= '9') //字符有效性
		{
			result = result * 10 + (*strNum - '0') * flag;
			if(result > 0x7fffffff || result < 0x80000000) //整形范围限定
			{
				g_bInvalidInput = true;
				resutl = 0;
				break;
			}
			strNum++;
		}
		else
		{
			g_bInvalidInput = true;
			result = 0;
			break;
		}
	}
	return (int)result;
}

【II】strcpy 字符串的复制从src到dst

/* [2].strcpy 字符串的复制从src到dst
* char* m_strcpy(char *dst, const char *src)
* @author arhaiyun
**/
char* m_strcpy(char *dst, const char *src)
{
	assert(dst != NULL && src != NULL);
	
	int srclen = strlen(src);
	//考虑地址重叠问题
	if(dst <= src || dst > src + srclen)
	{
		while((*dst++ = *src++) != '\0')
			NULL;
	}
	else
	{
		for(int i = srclen; i >= 0; i--)
		{
			*(dst + i) = *(src + i);
		}
	}

	return dst;
}

【III】strcat字符串连接

/* [3].strcat字符串连接
* char* m_strcat(char *dst, const char *src)
* @author arhaiyun
**/

char* m_strcat(char *dst, const char *src)
{
	assert(dst != NULL && src != NULL);
	
	char *pch = dst;
	while(*pch != '\0')
	{
		pch++;
	}	
	while(*src != '\0')
	{
		*pch++ = *src++;
	}
	*pch = '\0';

	//dst = m_strcpy(dst + strlen(dst), src); 另外一种实现方式
	
	return dst;
}